I've thought the same myself...but can you IMAGINE the outcry?
Why! That would be HORRIBLE! Discriminating! *gasp*
Because Ellis Island existed when there were no immigration quotas. Ellis Island was there to process all comers, and sort out the undesirables.
There is no point in an Ellis island now. There's no way anyone can show up at a legal point and get screened to get in.
Quotas and demand for US immigration in places like El Salvador are such that there are thirty-year waiting lists. That Salvadoran has no realistic hope of getting in legally, and if he did, by the time he go to the head of the line he wouldn't do the US much good, being in his fifties.